Protection Circuits; Power Supply Control Function; Energy Save Mode - Epson Stylus PHOTO 1270 Service Manual

EPSON Stylus Photo 870/1270

2.2.1.2 Protection Circuits

The C298PSB/PSE board has the various protection circuits to stop
voltage outputs if an abnormal condition relating to the control circuit or
the printer mechanism's duty occurs.
"
+42VDC Line Constant Voltage Control Circuit:
The output level of the +42V line is monitored by a detection circuit
composed of numbers of Zener diodes, and the information is fed
back to the primary side via photo coupler PC1. Along with the fed
back signal, the switching FET on the primary side varies the level of
the voltage output to the secondary side by changing its frequency to
keep the voltage up.
"
+42VDC line over current protection circuit:
If the +42 VDC line is over currented, the output voltage level drops
drastically. When the voltage level is 36V or lower, zener diode ZD90
detects that condition and sends information to the primary side via
photo coupler PC1. In the primary circuit, then, switching operation
stops to protect the electrical circuits and printer mechanism. To reset
the circuit, turn the printer off and back on.
"
+42VDC line over voltage protection circuit:
If the voltage level of the +42VDC line exceeds 59V, zener diodes D52
and ZD87 detect it and feed back the information to the primary side
via photo coupler PC1. The switching operation in the primary side
then stops to protect the electrical circuits and printer mechanism.
"
+5V line constant voltage/constant current control circuit:
Both +5V line output voltage and +5V line output current are
monitored by chopper IC (IC51). Detected information is input to the
IC's internal comparator and stabilizing circuit. When the IC detects
abnormally high current level, it stops outputting voltage. The circuit
recovers automatically.
"
+5V line over voltage protection circuit:
If the +5VDC output level exceeds 12V, zener diode ZD53 detects that
condition and feeds back the information to the primary side via
photo coupler PC1. The switching operation in the primary side then
stops to protect the electrical circuits and printer mechanism.
OPERATING PRINCIPLES

2.2.1.3 Power Supply Control Function

Since this printer has the power switch in the secondary circuit, even if its
power is turned off through the operation panel, it can continue to supply
voltage to the +5VDC line and +42VDC line for about 30 seconds. This
extra time allows the printer to complete the following operations:
"
If the printer is in a printing motion and the CR unit is out of its home
position, the printer stops printing, returns the CR unit to the home
position, and performs CR lock operation. Then the printer power
shuts down.
"
If the printer is not printing but paper loaded at ASF remains in the
printer, the printer ejects the paper before the printer power shuts
down.

2.2.1.4 Energy Save Mode

The power supply circuit enters the energy save mode by the signal
ESAVE sent from the control circuit. One the circuit is in this mode, it
maintains the +42V line level in a range from +20V to +23V.
Electrical Circuit Operating Principles
Revision B
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